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Statistical Study of Phase Relationship Between Magnetic and Plasma Pressures in the Near‐Earth Nightside Magnetosphere Using the THEMIS‐E Satellite
Author(s) -
Nishi Katsuki,
Shiokawa Kazuo,
Glassmeier KarlHeinz,
Mieth Johannes Z. D.
Publication year - 2018
Publication title -
journal of geophysical research: space physics
Language(s) - English
Resource type - Journals
eISSN - 2169-9402
pISSN - 2169-9380
DOI - 10.1029/2018ja025846
Subject(s) - magnetosphere , phase (matter) , plasma , physics , satellite , plasma sheet , atmospheric pressure plasma , geophysics , astrophysics , astronomy , nuclear physics , quantum mechanics
Distributions of plasma and magnetic pressures are the basic information to investigate macroscopic dynamics of the Earth's magnetosphere. Several studies have been made on magnetic and plasma pressures and macroscopic plasma instabilities in the magnetosphere. However, correlation between magnetic and plasma pressure variations has not been statistically investigated. In this paper, we analyze the statistical characteristics of the phase relationships between variations of magnetic and plasma pressures at frequencies of 4–15 mHz using 2 years of the THEMIS‐E satellite data in the nightside magnetosphere. Spectral peaks with coherence greater than 0.85 between magnetic and plasma pressures for 1‐hr time segments were selected. The average occurrence rates of the phase relationships are antiphase (within ±10 ∘ from 180°), 39.75%; in‐phase (within ±10 ∘ from 0°), 0.73%; and other phases (10–170°), 49.83%. For the other‐phase events, the phase differences are much closer to antiphase rather than to in‐phase. Thus, we conclude that the two pressure variations tend to be antiphase. The antiphase and in‐phase relationships are observed mainly at radial distances outside 8 R E and inside 8 R E , respectively. The high occurrence region of antiphase relationship is in the dawnside during magnetically quiet times and shifts to dusk side at active times defined as Dst <−10 nT. The occurrence rates of the phase relationships do not change significantly depending on the AE and Dst indices, plasma β , and IMF‐ B z . Based on these results, we discuss the correspondence between the phase relationships and the possible magnetohydrodynamic force balances that can produce these phase relationships.